Spinning of acrylonitrile polymers



Nov. 15, 1955 G. S. HOOPER 2,723,900

SPINNING OF' ACRYLONITRILE POLYMERS Filed DeC. 3, 1952 2 Sheets-Sheet l NOV- 15, 1955 G. s. HOOPER SPINNING OF ACRYLQNITRILE POLYMERS 2 Sheets-Sheet 2 Filed DGO. 3, 1952 United States Patent O ce 2,723,900 SPINNING oF ACRYLoNlrRmE PoLYMERs Gilman S. Hooper, Bay Village, Ohio, assignor to Industrial Rayon Corporation, Cleveland, (hio, a corpora` tion of Delaware Application December 3, 1952, Serial No. 323,757

22 Claims. (Cl. 18-454) This invention relates to an improved method of producing fibers, threads, yarns, tows and the like (hereinafter referred to as bers) by wet-spinning water-containing ethylene carbonate spinning solutions of acrylonitrile polymers and copolymers in an aqueous coagulating bath. More particularly, it is concerned with a method` for treating and processing the wet-spun freshly coagulated ber.

The Wet-spinning or wet-forming of ethylene carbonatesolvent type spinning solutions of acrylonitrile polymers was first described in the copending U. S. application of lohn M. .Terpay, Serial No. 245,697, filed September 8, 1951, issued August 30, 1955, as U. S. Patent No. 2,716,586. The invention described in that application is concerned with those conditions of the spinning solution and of the coagulating liquid bath which are necessary to achieve successful aqueous-bath spinning. Among other factors, it was established by that invention that ethylene carbonate-solvent spinning solutions of acrylonitrile polymers and copolymers, containing at least about 80% by weight of acrylonitrile 'in -the polymer molecule, could be extruded successfully into aqueous baths if certain amounts of water were incorporated in the ethylene carbonate spinning solution and if the aqueous coagulating liquid contained certain concentrations of ethylene carbonate.

The water-bath spinning process of the Terpay discovery (supra) provides a very simple system in which the only materials involved in the processing in addition to the polymer are water and ethylene carbonate. Furthermore, this process lends itself to a variety of aftertreating and regenerating methods and techniques. However, some difficulty is encountered which is believed largely due to the peculiar nature of the polymer solvent employed and the conditions under which it is used. vFor example, the solvent ethylene carbonate is an ester which is highly sensitive to water thus requiring very careful control of the aqueous regenerating conditions in order to achieve the desired ber properties. Moreover, this ester is quite susceptible to hydrolysis particularly when in contact with water for prolonged washing periods and especially at elevated temperatures. Accordingly, the fiber treatment process of this invention is directed particularly to those conditions under which the freshly coagulated fibers, made available by the Terpay discovery (supra), can be regenerated, oriented and water-washed free of the solvent while eiecting optimum economy with respect to ethylene carbonate; and while producing fibers of desirably high tensile strength and elongation and of low residual solvent content. Other advantages of the process will become apparent from the subsequent description.

The process in accordance with the present invention is as follows. comprising water, in an amount between about 2.5% and 18.5% by weight, and an acrylonitrile polymer or copolymer, containing in the polymer molecule at least about 80% by weight of acrylonitrile, is extruded into an aqueous coagulating liquid comprisingwa'ter and between 2,723,900 Patented Nov. 15, 1955 about 10% and 50% of ethylene carbonate solvent. The freshly coagulated fiber is withdrawn from the coagulant and is stretched. Some portion or all of the stretching operation is performed in a hot, above 80 C., aqueous liquid having a relatively low ethylene carbonate content, and preferably the fiber is kept in contact with the hot liquid for a short period of time. The hot-stretch liquid referred to contains ethylene carbonate at a concentration less than that of the coagulating liquid and preferably less than about 6% by weight. Advantageously, if desired, the freshly formed fiber may be given a stretch prior to the hot-stretch mentioned. The hot-stretched iiber is then subjected to an aqueous washing treatment which is hereinafter referred to as the intermediatewash. The aqueous washing liquid employed for the intermediate-wash contains ethylene carbonate at a concentration which is also less than that of the coagulating liquid but is greater than that of the liquid of the preceding hot-stretch treatment. The intermediate-wash liquid is prepared with part, and preferably all, of the eiuent resulting from the hot-stretch treatment. In an analogous manner, part, and preferably all, of the aqueous efliuent An ethylene carbonate spinning solution resulting from the intermediate-wash treatment is used to fortify or buck-up the coagulating liquid. In this manner the coagulant is fortified with water to compensate for the ethylene carbonate entering with the extruded spinning solution. The washed fiber resulting from the intermediate-wash treatment is then subjected to another wash treatment which is referred to hereinafter as the subsequent-wash. At least one of the aqueous liquids, and preferably, the last liquid applied to the fiber for said subsequent-wash treatment is a liquid which is substantially free from ethylene carbonate, e. g. water. Part and preferably all of the eluent resulting from the subsequent-wash, i. e. an aqueous liquid relatively low in ethylene carbonate, is diverted to be used in making up the hot-stretch treating liquid previously described. The resulting completely washed fiber is then in a suitable condition to be dried and collected directly or it may be collected after previously subjecting the fiber to any one or more aftertreatments as desired such as, for example, applying oil finishing agents, heat-relaxing, heat-treating, drying, crimping, cutting, etc.

As mentioned, the spinning solution suitable for successful practice of the process of the present invention is of the type described in the Terpay patent, supra. In addition to the polymer and ethylene carbonate solvent, such spinning solution contains water between about 2.5 and about 18.5% by weight, particular advantages being derived at between about 10% and 15%. The polymersolids content of the spinning solution may be between about 8% and about 30% by weight; superior results being obtained, however, with a solids content between about 12% and 18%. A reliable index of the spinnability of a given water-containing spinning solution of the type described is the cloud point. The cloud point as used herein is expressed as the temperature at which such a spinning solution changes from a cloudy or turbid solution to a clear transparent solution. The cloud point of the solution is a factor-in determining more suitable combinations of Solids, Water and solvent in the spinning solution and preferably should not exceed about 70 C.

The coagulating liquid into which the spinning solution is extruded comprises water and ethylene carbonate solvent in an amount between about 10% and 50% by weight, sampled at a point within three inches from the spinneret. Greater advantages are derived when employing coagulating liquids containing between about 20% and 38% ethylene carbonate solvent by Weight. It is Y found preferable to employ eoagulating liquids consisting temperatures. Yment may be performed in a narrow, shallow trough 3 lating -liquid is advantageously maintained at a temperature between about 40 C. and about 90 C.

V'Ihe fiber resulting from the extrusion of the spinning solution-into' the Vcoagulating liquid is withdrawn from the-coagulating liquid and before being subjected to the aqueous-hot-stretch treatment may, if desired, be given a'preliminary orientation by stretching so as to increase the totalover-all stretch, Preliminary stretches of at least about 150% or more of the original length of the ltiber'arefound highly advantageous. @Ast-indicated the hot-stretch treatment of the ii'oer is performed in a hot aqueous liquid which has a relatively `low ethylenefcarbonate content and is maintained at a temperature above about 80 C., optimum hot-stretching conditions being achieved at temperatures aboveabout 95 C. and preferably at the boil. Advantageously, the fiber is hot-stretched to a length 1.50% of its original length or greater if desired. In other words, a given length of fiber, that is, one meter, would be stretched to a total length of one and one-half meters or 150% of (l1/2 times) its original length.

The primary function of the hot-stretch treatment as employed in the present process is not as much concerned with any washing actionpas it-is to achieve the desired amount of orientation without either deleteriously affecting the character of the ber or adversely affecting the efficiency of the process. It is found that particularly advantageous results are derived when 'the amount of fiber-washing action of the hot-stretch liquid is minimized. lt is recognized, however, that somelincidental washing will of necessity occur. ln general, these stretching conditions are achieved by employing an aqueous hot-stretch liquid having a relatively low, yet a carefully controlled, ethylene carbonate content and also by minimizing advantageously the length of time both vthe fiber and the liquid are held at the elevated stretch temperatures prescribed.

Thus, for example, it is found that an aqueous hotstretch liquid containing too much ethylene carbonate is detrimental to the process. Among other eifects, it is found that there is under such conditions excessive hydrolysis-ofthe solvent at the temperature of the hotstretch treatment.y Hence, in practicing this invention, it isifound advantageous to employ aqueous hot-stretch liquids containing between about at least 0.5% and preferably less than by weight of ethylene carbonate.

YGreater advantages, however, are derived when the ethylene carbonate concentration is maintained between about 1%and 6%-by weight.

" vAs indicated, itis also advantageous to minimize the length of time both the iiber and the aqueous treating liquid are held at the elevated hot-stretch temperatures. In general, the vminimum time of contact of the fiber with therhot aqueous liquid is that time which is necessary to achieve the desired orientation, or more speciically, the minimum time required to heat the fiber to the optimum condition for stretching. This interval of time ymay vary depending upon the hot-stretch temperature employed and the denier of the yarn or tow undergoing hot-stretch orientation. Preferably, the time of Contact may be between about 0.2 to 2.5 seconds and most advantageously, less than one second. Thus, by mini- 4rnizing the contact time of the fiber and liquid in the heated stretch zone, the amount of washing action is advantageously reduced to a minimum and greater beneiits are derived.

Although various methods and techniques are available lfor achieving these desirable conditions, the follow- -ing technique is found quite advantageous for simultaneously controlling the ethylene carbonate concentration of the hot-stretch liquid, minimizing the amount of washing action on the fiber and also minimizing the contact time of both the liber and the liquid to the elevated Thus, for example, the hotstretch treat- :hot-stretch treatment of the preceding step.

or tube equipped with heating elements and designedv to contain the minimum operable volume of hot-stretch liquid. The liquid may be passed through the heated trough at a very rapid rate so as to maintain a positive control of the ethylene carbonate content of the liquid in the liber-liquid contact zone. The liquid is thereby quickly heated to the requisite temperature. With advantage, the liquid leaving the heated effective zone of the trough is thereafter rapidly cooled. Thus, the hotstretch liquid is vexposed to an elevated temperature for oni y a small interval of time. f

In practicing the process of this invention, it is found advantageous to maintain the residual ethylene carbonate content of the fiber entering the hot-stretch liquid at between about and 200% by weight, based on the weight of the dried iiber, while maintaining the residual ethylene carbonate content of the fiber leaving the hotstretch liquid at about 50% to 150%. Particular advantages are derived, however, when the fiber entering the hot-stretch liquid contains between about and 200% of residual vethylene carbonate.

In the intermediate-wash treatment which follows the hot-stretch treatment just described, the fiber is subjected to washing, in one or more stages, with an aqueous liquid which has a greater concentration of ethylene carbonate than the aqueous hot-stretch liquid and preferably, at least about 5% by weightless than that of the coagulating liquid. Thus, for example, if the coagulant contains y30% ethylene carbonate the intermediate-wash would contain less than 25% and the hot-stretch liquid less than about 10% and preferably less than about 6%. Greater advantages, however, are derived when the ethylene carbonate content of .the intermediate-wash liquidis maintained less than about 15% by weight. The .temperature ofthe intermediate-Wash liquid is advantageously` not greater than 60 C. and preferably, between about 40 and 60 C.

Particular benefits arederived when the duration ot the intermediate-wash treatment is such that the resultling washed fiber. upon withdrawal from the wash liquid described contains `between about 25% and 75% by weight of residual ethylene carbonate solvent.

In accordance with the present process, this intermediate-wash liquid is prepared with at least a portion, and preferably all, of the eiiluent resulting from the The intermediate-wash liquid `thus prepared is vapplied to the running iberso that it flows countercurrent to the direction 4of travel of ,theben Where a plurality of washing stages are employed to perform this step, the freshly prepared intermediate-wash liquid is rst introduced into .the last of suchv series of stages and flows to the first of: such stages. f

Analogously, as mentioned, part and preferably all, ,of ,the effluent resulting from the intermediate-wash. treatment is diverted to be incorporated into :the coagulating liquid for the purpose of fortifying orv bucking-up the latter to thereby maintain the coagulant at the desired water-to-ethylene..carbonate ratio. in practicing vthis invention it is found that this buck-up efliuent should contain no more than about 81,6. parts yby weightof water to eachpart by weight of spin solution extruded. Especial benefits are derived Vwhen this efuent contains at least about 5 parts by weight of water to cach part Vby weight of dry liber extruded. lt is highly advantageous for conditions to be such that the maintenaneerof the coagulating. liquid at the desired water-to-etliyiene carbonate ratio requires the ratio of water-to-dry fiber in the buck-up effluent from the intermediate-wash to be between about 7 andabout 26 parts by weight of water to'eachpart by wei'ghtpof Adrytiber extruded. in general, the-required ratio `of water-tosolvent diminishes the relative proportion of ethylenecarbonate inthe spinning solution decreases" orgthat in the coagulating liquid increases within the f'general'limits previously described therefor. UnderY these' conditions, 'relatively smaller quantities of buck-up eiiluent are required to compensate for the ethylene carbonate accumulation caused by the extrusion of the spinning solution into the coagulant.

Whatever portion of the aqueous efliuent resulting from the intermediate-wash treatment is not diverted as buckup for the coagulating liquid may, if desired, be by-passed directly to the solvent recovery system, alongV with the eiuent coming from the coagulating bath. These 'effluents are then subjected to a suitable recovery treatment to separate the ethylene carbonate solvent from the water. The recovered solvent, after being further purified, is suitable for appropriate re-use in the preparation of spinning solution.

The washed ber, after withdrawal from the intermediate-wash, is subjected to the subsequent-wash treatment of the present process. This washing step also may be performed in one or more stages and is effective in removing substantially all of the remaining quantities of residual solvent present in the ber. As mentioned, at least one of the last aqueous liquids applied to the be for the subsequent-wash treatment is a liquid which is substantially free from ethylene carbonate, e. g. water. Although higher temperatures may be employed if desired, the temperature of the subsequent-wash liquid is advantageously not greater than about 60 C. and preferably, between about 40 and 60 C.

At least a portion and preferably all of the eluent resulting from the subsequent-wash treatment just described is used to prepare the liquid for the hot-stretch treatment. The subsequent-wash effluent being diverted to the hot-stretch liquid is maintained at a relatively low concentration of ethylene carbonate, not greater than about 6% by weight and preferably, between about 1% and 3%.

The duration of the subsequent-wash treatment may be controlled so as to wash the ber substantially all of the residual solvent or, if desired, only part thereof. If desired, in connection with staple production, incompletely washed ber may be crimped and cut into staple and part of the subsequent-wash treatment may be performed on the ber in staple form. The present process is capable of producing, commercially and efciently, a washed ber containing less than about 3% by weight of residual solvent and if desired as low as 0.5 or less. Upon withdrawal from the subsequent-wash the washed ber ordinarily contains about 275% to 325% residual water. The finally washed ber thus produced is in condition suitable to be dried, aftertreated and collected as desired.

Advantageously, all of the water present in the aqueous processing system above described (with the exception of the water contained in the spinning solution), i, e. the water present in the coagulant, hot-stretch, intermediatewash and subsequent-wash liquids, is introduced as pure water substantially exclusively at one step of the process, namely, at the subsequent-washV treatment.v If desired, various amounts, and preferably small amounts, of water may also be introduced at any of the aqueous treatments mentioned, in order to make adjustments in the various ethylene carbonate-water ratios employed for the particular treating liquids concerned. It is particularly advantageous to introduce no more than about 81/2 parts by weight of over-all water for each part by weight of spinning solution extruded. VIt is also advantageous when at least about 6 parts by weight of water is admitted to the subsequent-wash to each part by weight of dry ber produced. Further, the greatest benets are derived and the process conducted with optimum result under such conditions that between about 8 and about 27 parts by weight of water is required to be admitted to the subsequent wash to each part of dry. ber produced without any other source of water save that contained inthe spinning solution. Especial benets are derived when the present process is performed on a completely-continuous basis, i.e. continuous ber treatment and with continuous liquid Cil ows from one liquid treatment step to the next as previously described and as more fully illustrated hereinafter. However, if desired, the ber treatment can be performed batch-wise on non-continuous lengths and with non-continuous liquid flows.

Suitable apparatus for the practice of the method of the present invention is illustrated in the accompanying drawings:

Figure l is a diagrammatic perspective view of an embodiment of the process useful for the continuous manufacture of textile yarns.

Figure 2 represents an embodiment adaptable for the continuous production of heavy denier yarns, tows and the like.

Referring to Figure 1, reference numeral 10 indicates a mass tube through which the spinning solution comprising polymer, solvent and water is conducted to the imrnersed multiholed spinneret 11 and thereby extruded into an aqueous coagulating bath 12 comprising ethylene carbonate solvent and water contained in trough 13. The resulting freshly formed, multilament yarn 15, after passing around guide 14, is withdrawn from the coagulating liquid 12 and conducted to and around thread-storage, thread-advancing device 18 and then to positively driven device 19 which is similar to 18 but driven at a greater peripheral speed thereby stretching the thread therebetween. The thread 15 leaving thread-advancing device 19 is hot-stretched by conducting it about spaced guides 20 and 21 immersed in hot aqueous bath 25 contained in a narrow, shallow trough 26 and then around roller guide 23 and onto a pair of positively driven, thread-storage, thread-advancing drums 30 and 31 rotating at a greater peripheral speed than the preceding thread-advancing device 19. The hot-stretch, aqueous bath 25, which is relatively low in ethylene carbonate, is heated to above C. by the heating coils 27, e. g. electrical or steam coils, located in the trough 26.

The resulting hot-stretched thread 15 which is advanced and stored as a helix about the pair of drums 30 and 31 is immersed in the aqueous bath 32 in trough 33 whereby the stored thread is subjected to the intermediatewash treatment. The intermediate-wash bath 32 is maintained at a temperature between about 40 and 60 C. and is made up with the aqueous eiuent resulting from the hot-stretch treatment. Thus, the etiiuent from the hot-stretch tmugh 26 is piped to trough 33 in order to replace the intermediate-wash bath 32 and thus buckup the water-to-ethylene carbonate ratio therein. The efuent from the intermediate-wash trough 33 is in turn passed through pipe 16 into the coagulating bath trough 13 in controlled quantities in order to buck-up the water ratio in a similar manner and thereby maintain the coagulating bath 12 at the desired composition.

The washed thread 15 leaving the thread-advancing drums 30 and 31 is then passed to and about another pair of thread-advancing drums 36 and 37 driven at about the same peripheral speed as the preceding drums 30 and 31. The pair of drums 36 and 37 are tilted upwardly in the direction of thread-advance so that any treating liquid applied thereto ows countercurrently to the direction of thread-advance and towards the thread-inlet end of the thread-advancing drums. Water 35 is applied to the helically stored thread by means of tube 34 positioned at the thread-discharge end of the thread-advancing drums. The resulting wash water discharged from the thread-advancing drums 36 and 37 is collected in trough 39 as subsequent-wash effluent 33 and contains a relatively low amount of ethylene carbonate. Eiuent 38 is piped to the hot-stretch trough 27 by means of pipe 40 so as to maintain the hot-stretch bath 25 at the low ethylene carbonate concentration desired.

The nally washed thread 15 leaving drums 36 and 37 is conducted to a third pair of thread-advancing drums 41 and 42 which are internally heated by any suitable means, e. g. electrical, steam, etc., so as to dry the thread helically stored. thereon. The dried thread leaving the heatedV drumsl is then passed through guide 43 and collected on bobbin 45` by means of cap-twisting device 44. The etiiuent' from the coagulating bath 12, containing a greater concentration of ethylene carbonate than the other aqueous treating liquids described, is diverted by pipe 46 to solvent recovery system 47 wherein ethylene carbonate 48 is separated from the water. The recovered ethylene carbonate may be recycled for making the spinning solution.

Referring to Figure 2, reference numeral 50 designates a spinningsolution preparation and storage system from which the water-containing spinning solution is passed through (one or more) mass tube 51 to be extruded through (one or more) multiholed spinneret 52 into aqueous coagulating liquid 53, in trough 54. The resulting freshly formed multitilament high-denier yarn 55 or tow, as the case may be, is withdrawn from coagulating liquid 53 about roller guide 56. The yarn, flattened in the form of a thin ribbon, is passed around a set of three yarn-gripping drums 59 positively driven at al predetermined peripheral speed and then around another set of drums 60 similar to the first set but driven at a greater peripheral speed so as to impart a stretch to the yarn between said sets of drums. The yarn 55 from the drums 60 is subjected to the hot-stretch treatment by passing it rapidly through the hot aqueous liquid 65 around spaced guides 63 and 64 in trough 66 and then looped once around each of a pair of drums 70 and succeeding pairs of drurns 74, 78, S3, 87 and 91 all of which are positively driven at the same greater peripheral speed than the preceding set of drums 60 so as to hot-stretch the yarn between drums 60 and 70. The hot aqueous liquid 65 is maintained at a temperature above about 80 C. by suitable heating means 62.

The hot-stretched yarn 55 is then subjected to the intermediate-wash treatment which is performed in six stages. The yarn is looped once, as mentioned, around each of six pairs of drums 70, 74, 78, S3, 87 and 91 in succession, the lower of each pair of drums passing through corresponding aqueous washing liquids 71, 75, 79, 84, S8 and 92.cont`ained in troughs 72, 76, S0, 85, 89, and 93 respectively. The yarn from the drums 73 is conducted to drums 83 by first passing it over roller guides 82 and 82A. The yarn moving from the iirst pair of drums 70 and .ultimately to the last pair of drums 91 travels countercurrently to the flow of the corresponding washing liquids while proceeding from trough to trough. Thus, the efiiuents 90, 86, 81, 77 and 73 from each of the series of intermediate-wash stages flow to the next preceding stage countercurrently to the direction of the yarn.

The aqueous washing liquid 92 present in the last of the series of intermediate-wash stages is made-up with, and replenished by, efuent 94 which is relatively low in ethylene carbonate content and which comes from the preceding hot-stretch treatment of the yarn. The hot eiuent 94 after leaving trough 66 is passed through a heat exchanger 95 to be cooled to between 40 and 60 C. before being used as the intermediate-wash liquid 92. Part of effluent 81 coming from the intermediate-wash liquid 84 may, if desired, be by-passed as effluent 68 to the multiport valve 67 and thence as coagulating liquid inuent 57 to coagulating liquid 53 while the balance of effluent S1 proceeds to the remaining intermediate-wash stages in order to replenish and replace wash liquids 79, 75 and 71 in succession and resulting finally in eiiiuent 69 leaving trough 72 which may likewise be diverted to valve 67 and thence as coagulating liquid influent 57 to coagulating liquid 53. if desired, however, eiiiuent 69 may be diverted directly through solvent recovery inlet feed 110 to be reclaimed in the solvent recovery system 112. Preferably, the coagulating liquid 53 is bucked-up solely. byeiuent 69 from the intermediate-wash and no portion of effluent 68 Afrom the stage of the intermediatewash in trough is used for this purpose. Coagulating liquid inliuent 57 from valve 67v which is composed of either efuent 69 or effluent 68 (which is a portion of efliuent S1), or both if desired, has a lesser concentration of ethylene carbonate solvent than coagulating liquid 53 so as to be useful for purposes of fortifying the coagulating liquid 53. In the instance when a portion of efiiuent 81 is diverted as effluent 68 to buck-up coagulating liquid 53 through influent 57, the remainder of the efliuent 81 picks up more ethylene carbonate from the yarn stored on drurns 78, 74, and 70 and the resulting effluent 69 may contain such a concentration of ethylene carbonate as to be useless for purposes of fortifying coagulating liquid 53. In such case, as mentioned, euent 69 is diverted directly to the solvent recovery system 112 through inlet. 110.

The yarn leaving drums 91, while still in the form of a thin flat ribbon, is then subjected to the subsequent-wash treatment which is performed in three stages. The yarn is looped once around each of three pairs of drums 97, 101 and 105 in succession, the lower of each pair of drums passing through corresponding aqueous wash liquids 98, 102, and 106 contained in troughs 99, 103, and 107 respectively. These aqueous wash liquids are maintained at a temperature between about 40 and 60 C. and originate from water 114 which is freshly introduced into trough 107 at the last stage of the subsequent-wash treatment. The resulting wash-liquid 106 flows from trough 107 in a direction counter to the direction of yarn travel through troughs 103 and 99 as stage efliuents 104 and to successively replace and replenish aqueous-wash liquids 102 and 98. Efuent 96 from the subsequent-wash treatment is passed through heat exchanger 95 to be heated by hot efuent 94 coming from the hot-stretch treatment and is thence used to replace and replenish the aqueous liquid 65 in the hot-stretch treatment.

The resulting yarn from the subsequent-wash treatment may be treated with oleaginous finishing agents, antistatic agents, etc., as desired either before or after it is conducted to the internally heated pair of drums 108 where it is dried.

Efuent 57 from coagulating liquid 53 is sent to the solvent recovery system 112 through solvent recovery feed inlet 110 along with any effluent such as effluent 69 from the intermediate-wash treatment. In the solvent recovery system 112 substantially pure ethylene carbonate is recovered by any suitable means. The recovered ethylene carbonate 113 isconducted to the spinning solution systern 50. If desired, it may iirst be decolorized and tiltered or otherwise treated so as to be suitable for re-use in preparing the spinning solution along with polymer 115 and spinning solution water 116.

The following examples illustrate specific embodiments of the invention although it is to be understood that there is no intention to restrict the invention to these illustrations. In these examples, parts and percent of materials, unless otherwise defined, means parts and percent by weight.

Example I In the manufacture of denier yarn, a spinning solution comprising 14 parts of polyacrylonitrile having an average molecular weight of about 40,000, 14 parts of demineralized water and 72 parts of ethylene carbonate solvent is prepared. The spinning solution has a cloud point of about 55 C. and is heated to about 70 C. for extrusion. Using the apparatus of Figure l, about 1.02 lbs. per hour of this spinning solution is extruded through mass tube 10 and spinneret 11 having 50 holes, each of 0.003 inch diameter, into coagulating liquid 12 contained in trough 13 consisting of about 67 parts of water and 33 parts of ethylene carbonate.

The coagulating liquid 12 is maintained at about 60 C.while the filaments, freshly formed at a rate of about 0.143 lb. of'dry fiber per hour, are drawn through the bath vfor a distance of about 58 inches. The thread 15 is withdrawn from the bath containing about 150% residual solvent and about 220% residual water and passed over positively driven thread-storage, thread-advancing device 18 being rotated at a peripheral speed of about 9.7` meters per minute. The thread is then passed in air to positively driven device 19, similar to 18 but rotated at a peripheral speed of about 44.6 meters per minute which imparts an initial stretch to the thread of about 460% of its original length.

Thread 15 is then hot stretched by passing it through hot aqueous liquid 25 for a distance of about 12 inches after which it is withdrawn by positively driven drums 30 and 31 being rotated at a peripheral speed of about 71.4 meters per minute so as to cause the liber to be additionally stretched to about 160% of its length while immersed in hot liquid 25, which has a relatively low ethylene carbonate content. Liquid 25 is composed of the etiluent from the subsequent-wash treatment in pipe 40 which contains about 2.0% ethylene carbonate. It is rapidly passed through trough 26, which has cross-sectional dimensions of 3%; inch width and 3 inch depth, at a rate of about 13.1 cc. per minute at the inlet. The immersion time of thread 15 in hot-stretch liquid 25 is between about 0.25 to 0.41 second. The over-all stretch imparted to the thread by initial orientation and by the hot-stretch treatment is about 736% of its original length. Aqueous liquid 25 is maintained at about 100 C. by means of steam coils 27 located at the bottom of trough 26. The residual solvent content of thread 15 upon being withdrawn from the hot-stretch treatment is about 105% and the residual water content about 275%.

The stretched thread 15 is then given the intermediatewash treatment by immersion in aqueous liquid 32 contained in trough 33 while being helically passed about positively driven thread-storage, thread-advancing drums 30 and 31. The distance of immersion is about 142 feet and the temperature of liquid 32 is maintained at about 60 C. Liquid 32 is made up with the elluent from the hot-stretch treatment which contains about 6.0% ethylene carbonate upon entering trough 33. The eluent from the intermediate-wash treatment, after washing thread 15, contains about 13.0% ethylene carbonate. This efuent is passed to fortify or buck-up coagulating liquid 12 through pipe 16 and contains about 11.4 parts of water to each part of polymer solids extruded through spinneret 11 per hour or about 1.60 parts of water to each part of spinning solution extruded per hour.

From drums 30 and 31 the thread 15 is withdrawn containing about 25% residual solvent and about 290% residual Water. The washed thread is helically passed about drums 36 and 37 operated by positive drive at the same peripheral speed as drums 30 and 31 whereon it is given the subsequent-wash with water 35, substantially free from ethylene carbonate, introduced through tube 34. The subsequent-wash treatment is performed at about V60 C. and the distance of immersion of the thread in the wash liquid is about 292 feet. Liquid 38 which collects in trough 39 underneath the drums 36 and 37 is passed through pipe 40 as effluent from the subsequent- Wash which, as mentioned, contains about 2.0% ethylene carbonate.

About 12.4 parts of water 35 are admitted in the subsequent-wash liquid to each part of solids extruded through spinneret 11 per hour or about 1.75 parts to each part of spinning solution extruded per hour. About 1.78 lbs. of water 35 is admitted through tube 34 per hour.

Washed thread 15 is withdrawn from the subsequentwash containing about 0.5% ethylene carbonate as residual solvent and about 300%` residual water. It is then passed about steam heated drums 41 and 42 whereon it is dried and heat-treated prior to being collected on bobbin 45 under cap twisting device 44.

The eluent from coagulating liquid 12 is diverted through pipe 46 to recovery system 47 wherein substantially pure ethylene carbonate 48 is recovered from aqueous solution. The recovered ethylene carbonate solvent 48 is suitable for re-use on a continuously recycled basis for the preparation of fresh spinning solution.

A colorless white liber is produced which is dense and free of objectionable voids on microscopic examination. It has a tenacity of about 3.3 grams per denier and an elongation at break of about 18%.

Example II Using the apparatus of Figure 2, a spinning solution comprising 13 parts of acrylonitrile having an average molecular weight of about 45,000, 14 parts of water and 73 parts of ethylene carbonate solvent is prepared in spinning solution system 50. The spinning solution has a cloud point of about 50 C.

In order to produce a yarn of about 44,000 denier, about 315 lbs. per hour of this spinning solution are extruded at about 70 C. through twenty mass tubes 51 and spinnerets 52 (each spinneret having 720 holes of 0.003 inch diameter) into coagulating liquid 53 contained in trough 54 consisting of about 30 parts ethylene carbonate solvent and 70V parts water and maintained at a temperature of about 65 C. The rate of extrusion through each spinneret is about 15.75 lbs. of spinning solution per hour. The resulting freshly formed multiiilament yarn 55 is withdrawn about roller guide 56 and flattened in the form of a thin ribbon. This ribbon of yarn 55 is passed to the positively driven yarn gripping drums 59 operated at a peripheral speed of 9.7 meters per minute. From drums 59 the yarn 55 is passed to another set of drums 60, similar to 59 but operated at a peripheral speed of 40.7 meters per minute so as to impart an initial stretch to the yarn of about 420% of its original length. At this point the yarn contains about 162% residual solvent and about 210% residual water. From the drums 60 the yarn is passed through hot aqueous liquid around guides 63 and 64 contained in trough 66 which has a cross-sectional height of three inches and a width of ten inches and then looped around drums 70 operated at a peripheral speed of 61.1 meters per minute thereby imparting an additional stretch to yarn 55 of about 150% of its length while the yarn is subjected to the hot-stretch treatment. Liquid 65 is maintained at C. by means of steam coils 62. The immei-sion distance of yarn 55 in liquid 65 is about l5 inches and the time of immersion is between about 0.375 to 0.53 second. Liquid 65 is composed of the effluent 96 from the subsequent-wash treatment which contains about 1.55% ethylene carbonate upon entry into trough 66. It is passed through trough 66 at a rate of about 1.21 gallons per minute. Eflluent 96 is heated by passage through heat exchanger 95 counter-current to eluent 94 from the hot-stretch treatment which is cooled thereby before being used in the intermediate-wash. Etlluent 94 from the hotstretch treatment contains about 5.12% ethylene carbonate.

Upon withdrawal from the hot-stretch treatment, yarn 55 contains about 112% ethylene carbonate as residual solvent and about 270% residual water. After leaving the hot stretch, the total stretch imparted to yarn 55 is about 630% of its original length.

Yarn 55 is then subjected to the six stage intermediatewash by being looped about drums 70, 74, 78, 83, S7 and 91 (all positively driven at a peripheral speed of 61.1 meters per minute) and passing for a total wash distance of feet in liquids '71, 75, 79, 84, 38 and 92 maintained at a temperature ofV about 50 C. and contained respectively in troughs 72, 76, 80, 85, 39 and 93. The intermediate-wash liquid moves from stage trough to stage trough as stage eiiluents 90, 86, 81, '77 and 73 in a direction counter to the progress of yarn 5S through the stages of the intermediate-Wash. The intermediate-wash is prepared by incorporating eluent 96 from the hot-stretch treatment (which, as mentioned, contains about 5.12% ethylene carbonate) in trough 93 as liquid 92. From the 75 last stage of the intermediate-wash the liquid washes yarn '5"unt-il"it-terrerges from'trough'n, the irststage of the intermediate-wash, as eiuent k69 which contains about 11.3% ethylene' carbonate. Effluent 69 'is diverted through valve v'67to coagulating 'liquid 53 so as to maintain in proper correlation the solvent and water constituents thereof. Effluent 6:9 contains about 14.2 parts water per part solid extruded through spinnerets 52 per hour or about 1.84 parts water .per part spinning solution extruded.

The yarn leaving drums 9i, still in the form of a thin flat ribbon contains about residual solvent and 280% residual water. it is passed through the subsequent-wash treatment by being looped around drums 97, 101 and 105 in succession and subjected for a total wash distance of 320 feet through the subsequent-wash liquids 9S, M2 and 106 maintained at about 50 C. and contained in troughs 99,5103 and 107 respectively. The subsequent-wash liquid is Composed of water 11'4 which, when introduced to the linal stage ofthe subsequent-wash in trough 107, is substantially free of ethylene carbonate. Liquid 106, which is composed of water 14 and tile ethylene carbonate washed from yarn '55 on drums E05 is passed as stage eilluent 104 to make-up 'liquid 102 in trough 103 which in turn 'is vpassed as stage eiiiuent litt) to make-up liquid 98 in trough 99. Effluent 55 from the subsequent- Wash treatment comes from the rfirst stage in trough 99 and, as indicated, contains about 1.55% ethylene carbonate. As mentioned, this effluent is passed through heat exchanger 95 'before 'being lused to ymalte-up liquid 65 in the :hot-stretch treatment. About 613 lbs. per hour of water 1.14 are admitted to the last stage of the subsequentwash in trough l0? which represents about 15.0 parts of water to'each part of solids extrudedthrough spinnerets 52 per `hour 'or about 1.95 parts of water to each part spinning solution extruded per hour.

Yarn 55 is Withdrawn from drums 105 containing about 2% residual solvent and about 290% residual water. The yarn is 'dried Von steam heated drums Hi8, then crimped, cut to staple and baled ready for shipment.

Efuent 57 from the coagulating liquid is sent to solvent recovery system M2 through solvent recovery inlet feed Il() wherein substantially pure ethylene carbonate solvent 133 is recovered-from aqueous solution. Recovered solvent 13 is continuously recycled to spinning solution system 50 for use in preparing fresh spinning solution. The recovered solvent may advantageously be decolorized with activated charcoal and tiltered continuously before re-use in the'process.

As is apparent, the yarn may be subjected to the wash treatments in any desired form. For example, it may be cutto staple lengths afterwithdrawal from the hot-stretch treatment and then subjected to the wash treatments in such form. 'it may be cut to staple after withdrawal from the'intermediate-washbefore being given 'the subsequentwash. Or, the yarnniay be cut to staple lengths during any part of the wash treatments, for example, it may be transformed from continuous filament lengths to staple forni after a portion of the subsequent-Wash treatment has been performed. l'n such cases, the balance of the wash treatment, particularly with regard to the employment of wash liquids and resulting efiluents, is performed on the staple according to the process of the invention. It is preferable, in any instance, to crimp the continuous filament yarn prior to cutting it into staple, however, if desired, the yarn may be crimped while in staple form after completion of the wash treatments. Other desirable treatments, physical or otherwise, may be performed on the yarn during any stage or interval of the wash treatments.

As is apparent from the foregoing description there are a number of modifications of the process which can be practiced without departing from the scope of the invention. Thus, for example, aqueous vtreating liquids, i. e. Water containing varying amounts of ethylene carbonate orl pure water, may be introduced at any of the described -tifeatin'giand washing steps for the purpose of 'adjusting vi2 either the ethylene carbonate content of the traveling thread or yarn, or the ethylene carbonate content of the various vaqueous treating liquids. Accordingly, minor amounts may be added for these purposes prior to the hot-stretch treatment or at any point after the hot-stretch treatment.

The ethylene carbonate solvent used in accordance with the process of the present invention, most advantageously, consists of substantially pure ethyiene carbonate. However, if desired, relatively small proportions of other compounds, preferably organic compounds, may be included therein provided they do not amount to more than about 5% by Weight of the ethylene carbonate present and, further, that they have no otherwise adverse eect upon the etiiciency of the process. Glycol compounds, e. g., ethylene glycol, dipropylene glycol, etc. are among the tolerable organic compounds which may be included in the ethylene carbonate solvent, with advantage.

As previously indicated, orientation stretching of the ber may be performed ata number of stages of the process in addition to the hot-stretch treatment of the present invention. Thus, preliminary orientation may be imparted to the fiber while it is still in the coagulating bath or, if desired, after it leaves the coagulating bath and while in air or in the presence of other aqueous treating liquids. Moreover, if additional orientation is desired after the hotstretch treatment the finally washed fiber, preferably containing little or no ethylene carbonate, may be stretched in the presence of steam.

Although greater advantages are derived in practicing the process of this invention in a continuous manner from start to finish with continuous flows of treating liquids from step to step, it is apparent that semi-continuous procedures can also be practiced if desired. Thus, for example, if higher extrusion speeds are desired the continuous length of yarn may be interrupted after the hot-stretch treatment and the yarn collected on a bobbin. Thereafter the washing treatments, i. e. the intermediate-wash and the subsequent-wash, may be performed at relatively lower speeds so as to reduce the size of the washing apparatus.

The recycling of the reusable ethylene carbonate is accomplished after subjecting the etti `cent from the coagulating bath to a recovery treatment. F.thus continuous portions of the bath may be subjected to a flash distillation under sub-atmospheric pressure so as to remove most of the water and the residue thereof thereafter fractionated to recover substantially pure ethylene carbonate solvent. The latter is then treated with decoiorizing carbon, filtered and recycled directly for use as solvent in the preparation of Aadditional quantities of spinning solution.

The spinning solution cloud point value which is referred to herein, and which was previously characterized as an index of good spinnability, is determined in the following manner. A solution containing the desired 'proportions of polymer, ethylene carbonate and water is Vheateduntil aclear, ktransparent solution is obtained. vThe'resulting solution is then permitted 'to cool slowly,

'with stirring, until the tirst signs of cloudiness appear.

The temperature atwhichthis change takes place is termed the cloud point. When employing solutions having a cloud point between about 20 and 70 C., the turbidity or cloudiness in the solution at the cloud point temperature is believed to vbe a precipitation of the polymer from the solution, whereas with solutions which are'still clear and non-turbid at about 20 C., the

turbidityor cloudiness which appears upon further cool- 'ing may be the same precipitation of the polymer component or -it may be a freezing or crystallization of the solvent component and more likely a combination of vrboth. yIn determining the cloud point, it is particularly important that the solution be cooled slowly. Ac-

cordingly, whenmaking cloud point'determinations, a cooling medium should Abe employed which is about 5 C.'lessthanfthe'temperatureof the solution beingcooled.

This invention may be utilized to produce a variety of final thread or yarn products, i e., threads having deniers as low as 75 to 50 or high-denier strands or tows for staple. Thus the process is found useful in making the high-denier strands, i. e. over 500 denier and up to 5,000 or more and is particularly useful for making tows of between about 40,000 and 1,000,000 denier. Moreover, these products can be produced at low speeds or more advantageously, at higher speeds ranging from 20 meters per minute or higher.

As previously stated, the proportion of acrylonitrile in the polymer molecule should be at least about 80% by weight and more advantageously, at least about 90% by weight. A minor proportion of one or more vinyl compounds can be copolymerized with the acrylonitrile, for example: vinyl esters (vinyl acetate, vinyl formate, vinyl benzoate), vinyl ethers, and vinyl ketones; acrylic acid and its esters and amides; methacrylic acid and its esters, amides, and nitrile; maleic, itaconic, fumaric, crotonic acids and their esters, amides and nitriles; allyl alcohol and its esters and ethers; styrene and nuclear substituted styrenes, e. g. chloroand dichloro-styrene; halogenated monoethylenic compounds such as vinyl chloride, vinyl fluoride, vinylidene chloride, 1,2-dichloropropene-1, 1,2-dichloro-propene-2, allyl chloride, methallyl chloride, 2-chloro-allyl alcohol, and l-allyloxy-3- chloro-Z-propanol; N-vinyl compounds such as N-vinyl pyrrolidone, N-vinyl succinimide, N-vinyl carbozole, N- tertiary butyl acrylamide, N-tertiary octyl acrylamide; 2- or 4-vinylpyridine; and the like.

The acrylonitrile polymers may be prepared by any suitable polymerization method such as, for example, polymerization with oxygen-yielding catalysts, e. g. benzoyl peroxide, hydrogen peroxide, tertiary butyl hydroperoxide, potassium or ammonium persulfate, etc. Redox polymerization systems employing oxygen-yielding catalysts such as the above in combination with reducing agents such as sodium bisulte, sodium hydrosulte, sodium formaldehyde sulfoxylate, etc., may also be used. Generally, after completion of the polymerization reaction, the resulting polymer is washed with water to remove any remaining impurities.

Although polymeric materials of higher molecular weight may be employed, those between 30,000 and 100,000 are preferred. The spinning solutions employed in the process of the present invention may be prepared by various methods. Thus, for example, one may prepare a room-temperature slurry of the polymer, ethylene carbonate and water and thereafter heat the slurry to etlect dissolution of the polymer. lf desired, the spinning solution may be prepared by rst preparing a polymer solution without the water consisting of ethylene carbonate and between about 15% and 25% of the polymer solids; deaerating this solution and then making the nal spinning solution by adding the desired quantity of water in the form of a water-ethylene carbonate mixture.

It is to be understood that all matter contained in the foregoing description be interpreted as illustrative merely and in no sense limiting since certain changes may be made in practicing the invention which in no way departs from its scope.

I claim:

1. In the method of making acrylonitrile polymer bers by extruding into a coagulating liquid comprising Water and between about 10% and 50% by weight of ethylene carbonate, a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by weight, andl a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, the steps comprising, withdrawing the resulting ber from said coagulating liquid; stretching said ber in the presence of an aqueous liquid maintained at a temperature above about 80 C., said hot aqueous stretching liquid comprising water and ethylene carbonate land having a lower concentration of ethylene carbonate than said coagulating liquid; withdrawing said stretched ber rom said hot-stretching liquid; subjecting said ber to an intermediate-wash treatment with an aqueous liquid comprising water and ethylene carbonate and having a lower concentration of ethylene carbonate than said coagulating liquid but greater than said hot-stretching liquid, said intermediate-wash liquid being prepared by incorporating at least a portion of the eiuent resulting from said hot-stretching treatment; diverting at least a portion of the eluent resulting from said intermediate-Wash treatment and fortifying said coagulating liquid therewith; subjecting said ber to a subsequent-wash treatment with an aqueous liquid which is substantially free from ethylene carbonate; diverting at least a portion of the efuent resulting from said subsequent-wash treatment and incorporating the same into the liquid used in said hot-stretch treatment. n

2. in the method of making acrylonitrile polymer bers by extruding into a coagulating liquid comprising water and between about 10% and 50% by weight of ethylene carbonate, a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by weight, and a polymer of acrylonitrile containing in the polymer molecule at least about by weight of acrylonitrile, the steps comprising, withdrawing the resulting ber from said coagulating liquid; stretching said ber in the presence of an aqueous liquid maintained at a temperature above about 80 C., said hot aqueous stretching liquid comprising water and ethylene carbonate and having a lower concentration of ethylene carbonate than said coagulating liquid; withdrawing said stretched ber from said hot-stretching liquid, subjecting said ber to an intermediate-wash treatment with an aqueous liquid comprising water and ethylene carbonate, said intermediate-wash liquid 'having a lower concentration of ethylene carbonate than said coagulating liquid but greater than said hot-stretching liquid, said intermediate-wash liquid being prepared by continuously incorporating at least a portion of the effluent resulting from said hot-stretching treatment; continuously diverting at least a portion of the eluent resulting from said intermediate-wash treatment and continuously fortifying said coagulating liquid therewith; subjecting said ber to a subsequent-wash treatment with an aqueous liquid which is substantially free from ethylene carbonate; continuously diverting at least a portion of the effluent resulting from said subsequent-wash treatment and incorporating the same in the liquid used in said hot-stretching treatment; drying said washed ber.

3. In the method of making acrylonitrile polymer bers by extruding into a. coagulating liquid comprising water and between about 10% and 50% by weight of ethylene carbonate, a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by weight, and a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, performing in a continuous manner and on a continuous length of ber the steps comprising, withdrawing the resulting ber from said coagulating liquid; streaching said ber to a lengthA at least about of its original length in the presence of an aqueous liquid maintained at a temperature above about 80 C., said hot aqueous stretching liquid comprising water and between about 0.5% and 10% by weight of ethylene carbonate; withdrawing said stretched ber from said hot-stretching liquid; subjecting said ber to an intermediate-wash treatment with an aqueous liquid comprising water and ethylene carbonate, and having a lower concentration of ethylene carbonate than said coagulating liquid but greater than said hot-stretching liquid, said intermediate-wash liquid being prepared by continuously incorporating at least a portion of the eluent resulting from said hot-stretching treatment; continuously diverting at least a portion of the eiiluent from said intermediate-wash treatment and continuously fortifying said coagulating liquid therewith so as to assist the maintenance of said coagulating liquid at said concentration, said diverted liquid containing less ethylene carbonate than said coagulating liquid; subjecting said ber to a subsequent-wash treatment with an aqueous liquid which is substantially free from ethylene carbonate; continuously diverting at least a portion of the ettluent resulting from said subsequent-Wash. treatment and incorporating the same in the liquid used in said hot-stretching treatment; drying said washed fiber.

4. A method according to claim 3 wherein the stretched liberV resulting from said hot-stretching treatment contains less than about 175% by weight of ethylene carbonate andthe fiber is stretched a total length of at least about 300% of the original length as withdrawn from the coagulating liquid.

5. A method according to claim 3 wherein the portion of the euent 4from the intermediate-wash treatment which is continuously diverted to fortify the coagulating liquid contains at least about ve parts by weight of water for each part by weight of said acrylonitrile polymer solids extruded into said coagulating liquid.

6. In the method of making acrylonitrile polymer bers by eXtruding into a coagulating liquid comprising water and between about 10% and 50% by weight of ethylene carbonate, a spinning solution comprising'ethylene carbonate, water in an amount between about 2.5% and 18.5% by weight, and a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, performing in a continuous manner and on a continuous length of ber thesteps comprising, withdrawing the resulting fiber from said coagulating liquid; orienting said ber by stretching it to a length at least about 150% of its original length; stretching said ber again to a length at least about 150% of its length while in the presence of an aqueous liquid maintained at a temperature above about 80 C., said hot aqueous stretching liquid comprising Water' and between about 0.5% and 10% by weight of ethylene carbonate; withdrawing said stretched ber fromr said hot-stretching liquid; subjecting said fiber to an intermediate-wash treatment with an aqueous liquid comprising water and ethylene carbonate and having a lower concentration of ethylene carbonate than said coagulating liquid but greater than said hot-stretching liquid, said intermediate-wash liquid being prepared by continuously incorporating at least a portion of the etlluent resulting from said hotstretching treatment; continuously diverting at least a portion of the etiluent from said intermediate-wash treatment and continuously fortifying saidcoagulating liquid therewith so as to assist the maintenance of said coagulating liquid at said concentration, said diverted liquid containing less ethylene carbonate than said coagulating liquid; subjecting said ber to a subsequent-wash treatment with an aqueous liquid which is substantially free from ethylene carbonate; continuously diverting at least a portion of the eiiiuent resulting from said subsequentwash treatment and incorporating the same into the liquid used in said hot-stretching treatment so as to'assist the maintenance of said hot-stretching liquid at said concentration; drying said washed fiber.

7. A method according to claim 6 wherein the stretched iiber resulting from said hot-stretching treatment contains less than about 175% by weight of ethylene carbonate and the fiber is stretched to a total length at least about 300% of the original length as withdrawn from the coagulatiug liquid.

8. in the method of makingacrylonitrile polymer bers by extruding into a coagulating liquidcomprising water and between about 10% and 50% by weight of ethylene carbonate, a spinning solution` comprising ethylene carbonate, water in an amount between about 2.5% and 118.5% by Weight, and a polymer of'acrylonitrile containing in the polymer molecule at least about by weight of acrylonitrile, performing in a continuous manner and on a continuous length of fiber the steps comprising, withdrawing the resulting iiber from said coagulating liquid; orienting said ber by streaching it to a length at least about 150% of its original length at a temperature below about 65 C.; stretching said liber to a length at least about 150% of its length while in the presence of an aqueous liquid maintained at a temperature above about C., said hot aqueous liquid comprising water and between about 1% and 6% by weight of ethylene carbonate; withdrawing said stretched liber from said hotstretching liquid; subjecting said fiber to an intermediatewash treatment with an aqueous liquid comprising water and ethylene carbonate while said ber is being conducted over at least one rotating thread-supporting device, said intermediate-wash liquid having a lower concentration of ethylene carbonate than said coagulating liquid but greater than said hot-stretching liquid, said intermediate-wash liquid being prepared by continuously incorporating at least a portion of the eilluent resulting from said hotstretching treatment; continuously diverting at least a portion of the eiuent from said intermediate-wash treatment and continuously fortifying said coagulating liquid therewith so as to maintain said coagulating liquid at said concentration, said diverted liquid containing less ethylene carbonate than said coagulating liquid; subjecting said fiber, While it is being conducted over at least one rotating thread-supporting device, to a subsequent-wash treatment with an aqueous liquid which is substantially free from ethylene carbonate; continuously diverting at least a portion of the eiuent resulting from said subsequent-wash treatment and incorporating the same in the liquid used in said hot-stretching treatment so as to assist the maintenance of said hot-stretching liquid at said concentration; drying said washed fiber.

9. A method according to claim 8 in which the fiber, which is conducted over the rotating thread-supporting devices for the performance of the intermediate and subsequent-wash treatments, is in the form of a helix; and in which the ber is washed substantially free of ethylene carbonate while being subjected to the subsequent-wash treatment.

10. A method according to claim S wherein the ilber is washed to no more than 3% by weight of ethylene carbonate after being subjected to the subsequent-wash treatment.

11. A method according to claim 6 in which the eiuent from the intermediate-wash treatment, which is being diverted for use in fortifying the aqueous coagulating liquid, contains ethylene carbonate in a concentration of at least about 5% by weight less than the concentration of ethylene carbonate in the coagulating liquid.

12. A method according to claim 6 in which the effluent from the subsequent-Wash treatment, which is being diverted for use in the hot-stretching treatment, contains less than about 3% by weight of ethylene carbonate; and in which the efiluent from the intermediate-wash treatment, which is being diverted for use in fortifying the aqueous coagulating liquid, contains ethylene carbonate in a concentration at least about 5% by weight less tha 1 the concentration of ethylene carbonate in the coagulating liquid.

13. A method according to claim 8 in which the effluent from the subsequent-wash treatment, which is being diverted for use in the hot-stretching treatment, contains less than about 3% by weight of ethylene carbonate; and in which the etlluent from the intermediate-wash treatment, which is being diverted for use in fortifying the aqueous coagulating liquid, contains ethylene carbonate in a concentration at least about 5% by weight less than the concentration of ethylene carbonate in the coaguiating liquid.

14. A method according to claim 6 in which substatitially all of the water present in all of the aqueous treat- 1'? ment steps recited from the coagulating step to the subsequent-wash treatment, with the exception of the water introduced by the spinning solution, is introduced at the subsequent-wash treatment step.

15. A method according to claim 8 in which substantially all of the water present in all of the aqueous treatment steps recited from the coagulating step to the subsequent-wash treatment, with the exception of the water introduced by the spinning solution, is introduced at the subsequent-wash treatment step.

16. A method according to claim 3 wherein the pertion of the eiuent from the intermediate-wash treatment, which is continuously diverted to fortify the coagulating liquid, contains no more than about eight and onehalf parts by weight of water for each part by weight cf spinning solution extruded.

17. A method according to claim 8 wherein the portion of the eiuent from the intermediate-wash treatment, which is continuously diverted to fortify the coagulating liquid, contains no more than about eight and one-half parts by weight of water for each part by weight of spinning solution extruded.

18. A method according to claim 17 wherein said portion of the etiiuent from the intermediate-wash treatment contains at least about iive parts by weight of water for each part by weight of said acrylonitrile polymer solids extruded into said coagulating liquid.

19. In the method of making acrylonitrile polymer fibers having a denier greater than about 2,000 by eX- truding into a coagulating liquid comprising water and between about 20% and 38% by weight of ethylene carbonate maintained at a temperature between about 40 and 90 C., a spinning solution maintained at a temperature between about 50 and 75 C. comprising ethylene carbonate, water in an amount between about and 15% by weight, and about 12% and 18% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, performing in a continuous manner and on a continuous length of fiber the steps comprising, withdrawing the resulting ber from said coagulating liquid; orienting said fiber by stretching itto a length at least about 150% of its original length at a temperature below about 100 C.; stretching said fiber to a length at least about 150% of its length while in the presence of an aqueous liquid maintained at a temperature above about 95 C., said hot liquid comprising water and between about 1% and 6% by weight of ethylene car-v bonate; withdrawing said stretched fiber from said hotstretching liquid; subjecting said iiber to an intermediatewash treatment with an aqueous liquid comprising water and ethylene carbonate, said intermediate-wash liquid having a concentration of ethylene carbonate greater than said hot-stretching liquidA and at least about 5% by weight less than the concentration of ethylene carbonate in said coagulating liquid, said intermediate-wash liquid being prepared by continuously incorporating therein the etiiuent resulting from said hot-stretching treatment; continuously diverting the eliiuent resulting from said intermediate-wash treatment and continuously fortifying said coagulating liquid therewith so as to maintain the coagulating liquid at said concentration; subjecting each part by dry weight of said fiber to a subsequent-wash treatment with between about eight and about twentyseven parts by weight of water which is substantially free from ethylene carbonate thereby washing said ber to less than about 3% by weight of residual ethylene carbonate; continuously diverting the eiliuent resulting from said subsequent-wash treatment and incorporating the same in the liquid used in said hot-stretching treatment; continuously recovering purified ethylene carbonate from the eiuent from said coagulating liquid; preparing at least a portion of said spinning solution with said 18 recovered ethylene carbonate; drying said washed fiber.

20. A method according to claim 19 in which the ber is stretched while being washed with the hot aqueous liquid for not more than one second and in which the fiber is washed to less than about 0.5% by weight of residual ethylene carbonate after being subjected to the subsequent-wash treatment.

21. ln the method of making acrylonitrile polymer fibers having a denier greater than about 2,000 by extruding into a coagulating liquid comprising water and between about 20% and 38% by weight of ethylene carbonate maintained at a temperature between about 40 and 90 C., a spinning solution maintained at a temperature between about 50 and 75 C. comprising ethylene carbonate, water in an amount between about 10% and 15% by weight, and about 12% and 18% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about by weight of acrylonitrile, performing in a continuous manner and on a continuous length of iiber the steps comprising, withdrawing the resulting fiber from said coagulating liquid; orienting said iiber by stretching it to a length at least about 150% of its original length at a temperature below about C.; stretching said iiber again to a length at least about of its length while in the presence of an aqueous liquid maintained at a temperature above about 95 C., said hot aqueous liquid comprising water and between about 1% and 6% by weight of ethylene carbonate; withdrawing said stretched iiber from said hot-stretching liquid; subjecting said ber to an intermediate-wash treatment with an aqueous liquid maintained at a temperature no greater than about 60 C. comprising water and ethylene carbonate, said intermediate-wash liquid having a concentration of ethylene carbonate greater than said hot-stretching liquid and at least about 5% by weight less than the concentration of ethylene carbonate in said coagulating liquid, said intermediate-wash liquid being prepared by continuously incorporating therein the effluent resulting from said hotstretching treatment after rapidly cooling said eliuent to the temperature of the intermediate-wash; continuously diverting the eiuent resulting from said intermediatewash treatment and continuously fortifying said coagulating liquid therewith so as to maintain the coagulating liquid at said concentration; subjecting each part by dry weight of said liber to a subsequent-wash treatment with between about eight and about twenty-seven parts by weight of water which is substantially free from ethylene carbonate maintained at a temperature no greater than about 60 C. thereby washing said fiber to less than about 3% by weight of residual ethylene carbonate; continuously diverting the etluent resulting from said subsequent-wash treatment and rapidly heating said eluent to a temperature above about 95 C. and incorporating the same in the liquid used in said hot-stretching treatment; continuously recovering purified ethylene carbonate from the eiuent from said coagulating liquid; preparing at least a portion of said spinning solution with said recovered ethylene carbonate; drying said washed ber.

22. A method according to claim 21 in which the fiber is stretched while being subjected to the hot-stretch liquid for not more than two and one-half seconds and in which the fiber is washed to less than about 0.5% by weight of ethylene carbonate after being subjected to the subsequent-wash treatment.

References Cited in the tile of this patent UNITED STATES PATENTS 2,530,962 Hare Nov. 21, 1950 2,570,257 McFarren Oct. 9, 1951 2,577,763 Hoxie Dec. 11, 1951 

1. IN THE METHOD OF MAKING ACRYLONITRILE POLYMER FIBERS BY EXTRUDING INTO A COAGULATING LIQUID COMPRISING WATER AND BETWEEN ABOUT 10% AND 50% BY WEIGHT OF ETHYLENE CARBONATE, A SPINNING SOLUTION COMPRISING ETHYLENE CARBONATE, WATER IN AN AMOUNT BETWEEN ABOUT 2.5% AND 18.5% BY WEIGHT, AND A POLYMER OF ACRYLONITRILE CONTAINING IN THE POLYMER MOLECULE AT LEAST ABOUT 80% BY WEIGHT OF ACRYLONITRILE, THE STEPS COMPRISING, WITHDRAWING THE RESULTING FIBER FROM SAID COAGULATING LIQUID; STRETCHING SAID FIBER IN THE PRESENCE OF AN AQUEOUS LIQUID MAINTAINED AT A TEMPERATURE ABOVE ABOUT 80* C., SAID HOT AQUEOUS STRETCHING LIQUID COMPRISING WATER AND ETHYLENE CARBONATE AND HAVING A LOWER CONCENTRATION OF ETHYLENE CARBONATE THAN SAID COAGULATING LIQUID; WITHDRAWING SAID STRETCHED FIBER FROM SAID HOT-STRETCHING LIQUID; SUBJECTING SAID FIBER TO AN INTERMEDIATE-WASH TREATMENT WITH AN AQUEOUS LIQUID COMPRISING WATER AND ETHYLENE CARBONATE AND HAVING A LOWER CONCENTRATION OF ETHYLENE CARBONATE THAN SAID COAGULATING LIQUID BUT GREATER THAN SAID HOT-STRETCHING LIQUID, SAID INTERMEDIATE-WASH LIQUID BEING PREPARED BY INCORPORATING AT LEAST A PORTION OF THE EFFLUENT RESULTING FROM SAID HOT-STRETCHING TREATMENT; DIVERTING AT LEAST A PORTION OF THE EFFLUENT RESULTING FROM SAID INTERMEDIATE-WASH TREATMENT AND FORTIFYING SAID COAGULATING LIQUID THEREWITH; SUBJECTING SAID FIBER TO A SUBSEQUENT-WASH TREATMENT WITH AN AQUEOUS LIQUID WHICH IS SUBSTANTIALLY FREE FROM ETHYLENE CARBONATE; DIVERTING AT LEAST A PORTION OF THE EFFLUENT RESULTING FROM SAID SUBSEQUENT-WASH TREATMENT AND INCORPORATING THE SAME INTO THE LIQUID USED IN SAID HOT-STRETCH TREATMENT. 